"can't stomach something" = to dislike or hate something
"I can't stomach his cooking. Every time I eat his soup, I get sick."

"eat like a horse" = to eat a lot
"My brother eats like a horse. He can eat 10 cheeseburgers in 15 minutes."

"mooch off of someone" = expect someone to pay your expenses
"Hey, now that you've turned 25, don't you think it's time to stop mooching off of mom and dad?"

"gym rat" = someone who spends a lot of time exercising at a gym
"My brother is a gym rat. He goes there every day after work for about three hours."

"fit as a fiddle" = to be in very good physical condition
"My grandfather is fit as a fiddle. He runs and hikes every morning before he goes to work."

"eat like a bird" = eat small portions
"Don't worry about spending too much money because she eats like a bird."

"be stuffed" = be full
"I'm stuffed, and I can't eat another bite."

"stick out like a sore thumb" = very visible because something is different
"If we don't follow the traditions, language, and body language of the culture, our actions might stick out like a sore thumb."